Dad not bonded with second child

First, this is my first post here, I've been reading around for a while and I hope I've picked an appropriate place to post this ..

We have two kids, a 3 y.o. daughter and a 16 months son.

My husband is really strongly attached to our first and their relationship and the way they interact is really wonderful. But he's basically found our son unfathomable/irritating/frustrating from the very beginning. He keeps saying "When he can talk..", but I fear that DD is just always going to be more interesting to Dad. DH is also convinced that he can step in at any time and start parenting the boy, because what happens now "doesn't matter", or more specifically, I guess, that it doesn't matter *who* does it.

It's frustrating and sad for me on so many levels, and some of them are kind of surprising. Like I'm jealous of the relationship DH has cultivated with DD, facilitated by my taking on all tending all of DS's needs. (DS is this fiery little ball of emotion and he feels SO big that it takes a lot holding and hugging and attention to keep him happy, and I feel like I'm losing major ground in my relationship with DD.)

So, does anyone have advice on facilitating DH relationship with our son, maybe some reference material to help convince DH that there is value to being present with DS now (though my own personal emotional state of feeling stretched thin will get me halfway, my husband is very scientific minded and evidence is always helpful), and maybe some help on how to maintain my relationship with my older daughter even while meeting the needs of her younger brother?